Hi is there a way to add an opt in check-box for wysija to a gravity form? Basically with this plugin users are added to your mailing list as they fill in the form, is there a way to give them an option to be subscribed or not?

Yes, when creating your feed from Gravity Forms to Wysija there is an option for an opt-in condition. You can set this so that someone is added to the newsletter only if they check a box, or select a specific option on the form. You may need to add a new checkbox to your form first.